I can't tell from the pic but on amc20's there were two carrier types. The smaller one works with the Richmond locker. The larger one does not as the spacing between the halves should be quite small. It appears you have a larger carrier and when the PO installed the locker, the halves are too far apart and have split out the locker. The main pin through the locker should be like 5/8 and on the larger carrier the pin is like 3/4". This spreads the locker halves as your picture shows so that the pins barely engage in the opposite half. I am betting the locker was installed on the wrong carrier.

I lived this one already. I had to buy a smaller carrier from Ebay to install the Richmond unit.